The present disclosure relates generally to bonding of dissimilar compositions. In particular, the disclosure relates to an improved method of bonding polyether block amide (PEBA) plastic composition with dissimilar compositions. The disclosure also relates to composite articles made by the method.
Consumers expect high performance from consumer goods. For example, articles of footwear have changed from fabric foot wraps and simple footwear, such as sandals and moccasins, to complex and sophisticated footwear designed for use in a particular sport or activity. This evolution is based in part on the availability of materials of construction, particularly synthetic materials not otherwise available in nature. Similarly, almost every other class of goods has evolved as materials of construction became more sophisticated.
Materials of construction are selected for their contribution to the article of manufacture. In addition to natural materials, such as wood, leather, and metal, many man-made compositions have become available. In particular, a man-made material has been developed as a substitute for almost every natural material. Some man-made materials essentially replaced the natural material (for example, polyamide essentially replaced silk in women's stockings) while other man-made materials are less successful replacements (such as poromeric materials as a leather substitute).
Polymeric materials such as plastics are widely available. Plastic materials may be thermoset or thermoplastic, elastic or plastic, and rigid or flexible, for example. The properties and characteristics of plastic materials are as varied as are the compositions. The varied properties of plastic materials may make combinations of materials especially useful.
For example, relatively elastic and relatively inelastic materials have been used in the construction of articles of footwear for many years. In particular, rubber materials have been widely used in the fabrication of midsoles and outsoles of articles of footwear. Rubber and plastic elements frequently are placed in direct communication with one another in the fabrication of an article of footwear with conventional fixation methods including stitching, riveting, screwing, nailing, and the use of various adhesives.
These methods of fixation achieve the object of combination with varied degrees of success. For example, use of adhesives requires careful selection. Adhesives typically are selected to be compatible with each of the substrates to be attached lest the substrates be damaged by the adhesive. For example, adhesives comprising solvents may mar the surface of the substrates. Similarly, other conventional fixation methods may cause weak areas in the materials in the area of the piercing required to stitch, nail, or rivet items, for example.
Direct injection of plastic onto rubber, leather, and many of the natural and synthetic textiles also is known, particularly in footwear manufacture. Direct injection may form a mechanical bond prone to delamination of plastic from the other material as the result of bond failure induced by fatigue and environmental degradation.
Chemical (covalent) bonding and co-vulcanization may be effective between specific rubber and plastic articles. Also, vulcanization is known in the art as a means of attaching shoe portions to each other. However, the dissimilar properties of rubbers and thermoplastics and thermoplastic elastomers result from different chemical properties and characteristics, thus making vulcanization of one to the other without pretreatment of one or both substrates problematic to achieve.
In footwear, performance properties and characteristics relating to parts of the footwear are important. For example, in some specific utilities, the shoe sole should be flexible and resistant to wear. In such cases, rubber ground-engaging segments may be placed on the bottom of an outsole, or flexible rubber inserts may be used between more rigid sole segments. However, these combinations have been limited to a few combinations of materials that both have the properties and characteristics necessary to provide the properties and characteristics expected and may be durably bonded together.
Footwear outsoles comprised entirely of rigid plastic materials may be inappropriate for some articles of footwear, i.e., athletic footwear such as shoes for running, basketball, tennis, racquetball, etc. The rigidity, weight, and lack of traction of such materials may render outsoles comprised entirely of rigid plastic materials less suitable for use in some athletic footwear. Although rubber may be a more appropriate choice for an outsole of footwear for activities that require good traction, outsoles comprised entirely of rubber materials for articles of footwear may lack necessary support for some uses.
Thus, there exists a need for an article of footwear that comprises an outsole having different materials having selected physical and mechanical properties in different regions, and wherein these materials are adequately bonded to one another. There exists a need to provide a flexible, light, and durable articles, particularly soles for use in an article of footwear. Additionally, there is a need to provide an efficient, economical, and low-emission method for bonding relatively elastic and relatively inelastic materials.